The evaluation of retinal structure as determined by photographic documentation at the three-month follow-up examination has indicated a favorable outcome in eyes treated in the CRYO-ROP trial. This outcome makes follow-up of infants in the CRYO-ROP trial essential to evaluate the long-term safety and efficacy of the procedure, to determine the optimal disease threshold for application of the therapy, and to define the indications for routine follow-up of infants with mild ROP. The primary outcome measure of the CRYO-ROP study was the status of the retinal structure, as determined by photographic documentation at one year after cryotherapy. During the time since intake of patients for the trial began in 1986, the technology for4 measuring visual function in infants evolved to the point that it was possible to add a second outcome measure at one year after cryotherapy. This second outcome measure is grating visual acuity, as assessed monocularly by Teller Acuity Cards. We propose to continue to evaluate retinal structure and visual function in infants in the CRYO-ROP trial for an additional five- year follow-up period in order to attempt for the first time to correlate the structural changes observed in both the acute proliferative and the scarring phases of ROP with the eventual visual function of the eye. We will also evaluate the long-term risk/benefit ratio of recommending cryotherapy in infants with differing degrees of ROP and document the long-term eye status and visual function of very low birthweight infants with varying degrees of treated or untreated ROP. The Visual Acuity Center will train eight testers in methods of assessing functional vision (resolution acuity, recognition acuity, and visual fields) of children in the study, will monitor the activities of the testers as they test all randomized and natural history patients at the 23 centers participating in the study, will assure that quality control is maintained, and will participate in data analysis and writing of manuscripts related to visual function in the study population.